The results showed a community that was both similar to and different from modern human gut microbiomes in ways that illuminate how human gut biology has changed over five thousand years.

The Helicobacter pylori bacteria found in Ötzi’s gut — the pathogen associated with gastric ulcers — was particularly interesting.

Genetic analysis of this ancient H. pylori strain revealed it to be a form distinct from the dominant modern European H. pylori strains, which show extensive mixing between Asian and European varieties. Ötzi’s H. pylori strain was predominantly Asian in its genetic character, without the European admixture that characterizes modern European strains — suggesting that the European H. pylori population was less genetically mixed in the Copper Age than it is today.

This finding about a single bacterium in one individual’s gut has implications for the much larger question of when different populations of humans came into contact with each other sufficiently to mix their gut bacteria.